Chemical, physical and biological properties of alginates and their biomedical implications

Alginates are binary, linear copolymers of (1 → 4) linked ß-d-mannuronic acid (M) and α-l-guluronic acid (G) residues of widely different composition and sequence. The monomers do not occur randomly but rather in a block-like fashion, where the G-blocks are responsible for the specific ion binding and hence also the gelling properties of alginates. Alginates have for decades been used as medical devices in various products, and research has been conducted on alginate gel beads as entrapment devices for the transplantation of e.g. insulin producing cells. Until recently, no pharmaceutical activity of the alginate molecule itself had been claimed. The fact that alginates high in mannuronate residues are able to induce cytokine production and may stimulate Toll-like receptors has changed this picture. Furthermore, it has quite recently also been shown that oligoguluronates are able to transiently modify mucin network structures to such an extent that it opens up possibilities for the treatment of pathological respiratory diseases as well as a general increased drug bioavailability due to increased mucosal uptake. This review presents a summary of the physicochemical properties of alginates and their entry into biotechnology and biomedicine.